Dense gas in nearby galaxies Lebrón, M.; Mangum, J. G.; Mauersberger, R. ...
Astronomy and astrophysics (Berlin),
10/2011, Letnik:
534
Journal Article
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Context. The central few 100 pc of galaxies often contain large amounts of molecular gas. The chemical and physical properties of these extragalactic star formation regions differ from those in ...galactic disks, but are poorly constrained. Aims. This study aims to develop a better knowledge of the spatial distribution and kinetic temperature of the dense neutral gas associated with the nuclear regions of three prototypical spiral galaxies, NGC 253, IC 342, and Maffei 2. Methods. VLA CnD and D configuration measurements have been made of three ammonia (NH3) inversion transitions. Results. The (J,K) = (1, 1) and (2, 2) transitions of NH3 were imaged toward IC 342 and Maffei 2. The (3, 3) transition was imaged toward NGC 253. The entire flux obtained from single-antenna measurements is recovered for all three galaxies observed. Derived lower limits to the kinetic temperatures determined for the giant molecular clouds in the centers of these galaxies are between 25 and 50 K. There is good agreement between the distributions of NH3 and other H2 tracers, such as rare CO isotopologues or HCN, suggesting that NH3 is representative of the distribution of dense gas. The “Western Peak” in IC 342 is seen in the (6, 6) line but not in lower transitions, suggesting maser emission in the (6, 6) transition.
The dwarf galaxies in the Local Group (LG) reveal a surprising amount of spatial structuring. In particular, almost all non-satellite dwarfs belong to one of two planes that show a very pronounced ...symmetry. In order to determine if these structures in the LG are dynamically stable or, alternatively, if they only represent transient alignments, proper motion measurements of these galaxies are required. A viable method to derive proper motions is offered by VLBI studies of 22-GHz water (and 6.7-GHz methanol) maser lines in star-forming regions. In 2016, in the framework of the Early Science Program of the Sardinia Radio Telescope (SRT), we have conducted an extensive observational campaign to map the entire optical body of all the LG dwarf galaxies that belong to the two planes, at C and K band, in a search for methanol and water maser emission. Here, we outline the project and present its first results on 3 targets, NGC 6822, IC 1613, and WLM. While no luminous maser emission has been detected in these galaxies, a number of interesting weaker detections has been obtained, associated with particularly active star forming regions. In addition, we have produced deep radio continuum maps for these galaxies, aimed at investigating their star forming activity and providing an improved assessment of star formation rates in these galaxies.
Dielectric thin films of Formula Omitted deposited by atomic layer deposition (ALD) are investigated to be employed in Ge Schottky barrier p-MOSFETs. Formula Omitted is used as a thin passivation ...layer and is capped by atomic-layer-deposited Formula Omitted as a gate dielectric. As the gate contact TiN capped by W is applied, midgap-level trap densities of Formula Omitted and subtreshold slopes down to 115-120 mV/dec are achieved. The devices show negative threshold voltages of Formula Omitted0.5 to Formula Omitted0.6 V, as well as peak hole mobility values of Formula Omitted50-75 Formula Omitted. Equivalent oxide thickness (EOT) is reduced to 0.96 nm upon postmetallization annealing without degrading the interface properties. The results show the scaling potential of the ALD Formula Omitted interlayer capped with Formula Omitted gate dielectrics for the integration into sub-1-nm EOT Ge p-MOSFET devices.
Dielectric thin films of hbox La 2 hbox O 3 / hbox ZrO 2 deposited by atomic layer deposition (ALD) are investigated to be employed in Ge Schottky barrier p-MOSFETs. hbox La 2 hbox O 3 is used as a ...thin passivation layer and is capped by atomic-layer-deposited hbox ZrO 2 as a gate dielectric. As the gate contact TiN capped by W is applied, midgap-level trap densities of similar to hbox 3 - hbox 4 hbox 10 12 Unknown character hbox eV - 1 Unknown character hbox cm - 2 and subtreshold slopes down to 115-120 mV/dec are achieved. The devices show negative threshold voltages of - 0.5 to - 0.6 V, as well as peak hole mobility values of similar to 50-75 hbox cm 2 / hbox V times hbox s . Equivalent oxide thickness (EOT) is reduced to 0.96 nm upon postmetallization annealing without degrading the interface properties. The results show the scaling potential of the ALD hbox La 2 hbox O 3 interlayer capped with hbox ZrO 2 gate dielectrics for the integration into sub-1-nm EOT Ge p-MOSFET devices.
The laterality of projections from the lateral superior olivary nucleus (LSO) to the inferior colliculus was studied in adult and immature postnatal ferrets. In the adult ferret, large unilateral ...injections of horseradish peroxidase (HRP) in the inferior colliculus labeled about equal proportions of cells in the ipsilateral and contralateral lateral superior olivary nuclei. The contralateral labeled cells consistently were more densely labeled than those on the ipsilateral side. Double labeling experiments using fluorescent dyes indicated that only about 3% of LSO cells in the adult give rise to collaterals ending in the inferior colliculus on both sides. As expected, the distribution of labeled cells varied topographically in the LSO as a function of the injection site in the inferior colliculus. Dorsolateral inferior collicular injections labeled cells in the lateral limb of the LSO, whereas ventromedial injections labeled cells in the medial limb of the LSO. The proportion of ipsilateral and contralateral labeled cells also varied across the lateral-medial axis of the LSO in some cases. A gradient in laterality was observed in these cases with the lateral limb of the LSO containing the highest proportion of contralateral labeled cells, and the medial limb, the highest proportion of ipsilateral labeled cells. Larger inferior collicular injections resulted in greater proportions of ipsilateral labeling in LSO than smaller injections. Finally, ipsilateral labeled cells tended to be in the marginal region of the LSO, whereas contralateral labeled cells were more common within the core region of the LSO, irrespective of the location along the lateral-medial axis of LSO. The contralateral predominance of labeled cells, greater density of labeling in contralateral cells, different topographic distribution, and regional segregation of ipsilateral and contralateral labeled cells were typical of the LSO in ferret kits by birth, one month before the onset of hearing. Nevertheless, the relative proportion of ipsilateral and contralateral projection cells appears to change during postnatal development.
Subdivisions of the cochlear nuclear complex give rise to a number of discrete projections to certain cell groups of the superior olivary complex and also received substantial descending projections ...from the periolivary nuclei. In the present study, we sought to determine by means of retrograde transport of horseradish peroxidase (HRP), and anterograde transport of radiolabeled protein, if the periolivary nuclei give rise to discrete projections to the various subdivisions of the cochlear nuclear complex. Following medium to large injections of HRP into the cochlear nucleus, irrespective of location, labeled cells were found in all periolivary nuclei bilaterally. In every case more than 40% of the labeled cells were found in the lateral nucleus of the trapezoid body on the same side and the ventral nucleus of the trapezoid body of both sides. Other periolivary nuclei contributing more than 5% of the total number of cells in individual cases were the contralateral lateral nucleus of the trapezoid body and the ipsilateral anterolateral and dorsal periolivary nuclei. Injections of tritiated leucine into periolivary nuclei gave rise to axonal labeling to the trapezoid body and the dorsal acoustic stria, usually bilaterally, and to terminal labeling that was widely distributed within the cochlear nuclear complex. In several cases with small injections, particularly in the lateral nucleus of the trapezoid body, the projections from the periolivary nuclei to the anteroventral and dorsal cochlear nuclei connected areas described as having similar best-frequency representation. The autoradiographic data corroborated the main results from the HRP experiments and provided additional information permitting these conclusions: the projections from the periolivary nuclei to the cochlear nuclear complex are organized tonotopically, at least in part; each periolivary nucleus (and perhaps individual cells), projects widely throughout the cochlear nuclear complex; the pattern of termination of projections from different periolivary nuclei to a given region of the cochlear nuclear complex are similar, as seen in autoradiograms, and the lateral and dorsal periolivary nuclei project mainly ipsilaterally, while the medial periolivary nuclei project bilaterally with a contralateral bias. The magnitude of these projections and their widespread distribution within the cochlear nuclear complex would suggest an important role for the descending projections in the normal functioning of the cochlear nucleus.
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